The goal of the proposed research is to gain information on the physiology and biochemistry of insulin in the aqueous and vitreous of rabbits. These studies will be based upon a radioimmunoassay procedure for insulin which takes into account that the physiological levels of insulin in the ocular fluids are substantially less than in blood. Insulin in aqueous and vitreous will be measured under a variety of conditions classically known to affect insulin levels in blood: fasting, feeding, glucose challenge, tolbutamide challenge, alloxan diabetes. Preliminary experiments by the principal investigator indicate that the insulin concentration in aqueous humor is approximately 1 percent of the plasma concentration and increases in response to feeding. Since insulin in the ocular fluids may play a role in diabetic cataract, diabetic retinopathy, and possibly other eye pathology, basic knowledge concerning insulin in the ocular fluids, such as these investigations are designed to furnish, may lead to more effective ophthalmologic management of persons afflicted with diabetes.